One server that uses every primitive, runs over both transports, sits behind auth, and is tested end to end, with one annotated trace through all of it

The plumbing every MCP primitive shares: how a long call reports progress, how either side cancels one, how a connection is checked, how a list is paged

The 2025-11-25 initialize exchange, hand-rolled in Go against a real server. Later revisions dropped it from the protocol core.

Three message shapes, one error object, and a hundred and fifty lines of Go that every MCP transport is built on

The Go SDK never prints the protocol. This post does.